Exposing the public to water contaminated with microorganisms, which includes drinking water and non-drinking water, represents a serious health problem. There is a general need for improved materials and methods to eliminate microorganisms from fluids for various applications, including the provision of safe or potable drinking water as well as the provision of microorganism-free water to various devices or systems, which include drinking water treatment plants, air conditioning systems and swimming pools.
Biocidal agents commonly used in water disinfection encompass halogens, ozone, U.V., quaternary amine compounds, hydrogen peroxide, sodium monopersulphate, and metal ions.
The use of metals for water disinfection is known from antiquity, and has recently increased, due notably to the fact that microorganisms have acquired resistance to usual treatments. The biostatic/biocidal properties of metal ions such as silver, copper and zinc are well known in the art. Antimicrobial effects of metal ions have been shown in the art for a variety of bacteria (including E. coli, S. aureus, S. epidermis, S. pneumoniae, P. aeruginosa), viruses (including Herpes simplex, HIV, Nile virus), fungi (A. niger, C. albicans) and micro-algae. So far, metal ions have been used for this purpose under various forms, such as metal colloids (salts, oxides) or alloys. In some prior art embodiments, water treatment using metal ions was performed using metal salts, in which case the rapid consumption of the ions reduced the longevity of the disinfectant effect. Notably, metal ions are readily complexed with organic matter in the contaminated water and they become unavailable for killing microorganisms. According to the prior art methods, a continuous production of metal ions was needed to generate an effective and long term antimicrobial effect.
Owing to their strong oxidant properties, cationic forms of various heavy metals such as As+, Pb2+, Cd2+, Hg2+ and Cr6+ have been discussed for their toxicity towards microorganisms. The antimicrobial activity of these cationic entities has been ascribed to their electron attraction effect upon contact with the microorganism membranes inducing membrane alterations that cause the death of the microorganisms.
Sterilizing power of other metals such as copper, gold and platinum was also known in the art. Also, colloidal silver is widely recognized in the art as a relevant antimicrobial agent. It has been shown in the art that silver is active at least against 650 distinct microorganisms species, which allows to classify silver as a broad spectrum antimicrobial agent. It is noticed that silver particles have been used in the art as antibiotic active ingredient. Silver has been shown to be effective against numerous pathogenic bacteria, including antibiotics-resistant pathogenic bacteria, as well as numerous protozoa and viruses.
Silver has also been reported to delay or prevent the formation of biofilms in medical catheters, prosthetic heart valves, vascular grafts and fracture fixation devices. Silver has also been used in water filters, cooling towers and water distribution systems. In all these applications, silver exerts its antimicrobial effect by progressive elution from the devices.
Noticeably, silver released under the form of its silver nitrate salt has been found ineffective to prevent biofilm formation in water distribution systems (Silvestry-Rodriguez et al., 2008, Applied and Environmental Microbiology, Vol. 74 (no 5): 1639-1641).
Actual mechanisms that underlie the microbicidal effect of silver have not yet been unequivocally deciphered. Some authors have shown that the bactericidal activity of silver is mediated by its binding to disulfide or sulfhydryl groups in cell wall proteins. Other authors have shown that silver also binds to DNA. According to some scientific works, silver must be under its ionized form, i.e. in its cationic form, to exert antimicrobial properties (Lok et al., 2007, Journal of Biological inorganic Chemistry, Vol. 12 (no 4): 527-534; Rai et al., 2009, Biotechnology Advances, Vol. 27: 76-83).
There is still a need in the art for alternative or improved antimicrobial materials and systems for the purpose of treatment of various fluids, particularly aqueous media, including water.